A coalition of public and private environmental experts continues to monitor the effects of a Sept. 29 diesel spill near the Lochsa River on U.S. 12., although activity will be limited by the arrival of winter weather.

The contractors (working on behalf of trucking company Keller Transport) will continue to operate and monitor recovery wells drilled near the highway and Lochsa River through the winter. A 1,000-foot boom designed to contain sheen in the river has been removed for safety considerations. Several other booms remain in place to limit the intrusion of diesel into the river.

"We continue to see a light sheen and a very small amount of product emerging from two locations along the river bank," said Gayle Westhoff of the Idaho Department of Environmental Quality (IDEQ). "Absorbent booms and pads are in place at these locations along with a single 100-foot hard boom just beyond these two remaining fuel/sheen emergent areas."

An estimated 7,500 gallons of diesel spilled into a borrow pit north of the highway after the driver lost control of his tanker truck and trailer. The tank ruptured when it hit a rock ledge about 136 miles east of Lewiston.

The Idaho Transportation Department (ITD), one of the responding agencies, reduced the highway to a single lane following the crash to facilitate excavation and removal of soil from the borrow pit.

Initial response efforts also focused on the deployment of booms in the Lochsa River and absorbent pads at the highway embankment. It also included extensive efforts to locate the subsurface migration route of diesel from the spill location.

"The highway road cut crosses granitic bedrock. The bedrock is covered by three to 25 feet of alluvial gravel cobles and boulders, and probably some shot rock from the highway cut," Westhoff explains.

"Finding the product's location has been and continues to be a challenge."

Three 2-inch recovery wells were bored in the U.S. 12 westbound lane to a depth of more than 50 feet. A small amount of diesel was recovered from those wells before they were abandoned and filled recently. The lane was reopened and the highway restored to unrestricted traffic in both directions late last week.

Six other extraction wells, each four inches in diameter, were drilled in soil near the river. Automatic skimmers have been installed in three of these wells to remove diesel from the surface of water at a depth of about 50 feet. Skimming will continue through the winter and will be evaluated in the spring for the effectiveness of the diesel recovery, Westhoff said.

Agencies involved in monitoring cleanup efforts include IDEQ, ITD, the U.S. Forest Service, the U.S. Environmental Protection Agency and the Idaho State Police. Representatives will continue to visit the site throughout the winter to observe and discuss ongoing and proposed site activities, Westhoff added.

Herrygers International Environmental Services of South Carolina is consulting with public agencies on cleanup efforts.